Photographic emulsion



13422419410. -ERDAVEY 2,226,158

' PHOTOGRAPHI C EMULS ION Filed May 9, 1939 A YS vPatented Dec; 24, 1940v UNITED STATES IATEN T OFFICE i PHOTOGRAPHIC EMULSION Edward P. Davey, Harrow, England, assignor to Eastman Kodak Company. Rochester, N. Y., a

- v corporation oi' New Jersey Application May 9, 1939, Serial No. 272,653

11 Claims.

This invention relates to sensitized photomaterials which in themselves do not materially spectrally sensitize photographic emulsions, but which, when mixed or combinedA with the spectrally sensitizing materials, act 'to increase the' sensitization produced by the spectrally sensitizing materials alone.

It is known in the art of making photographic emulsion-s that certain dyes of the cyaniue class y alter the sensitivity of photographic emulsions of the silverhalide kind, when the dyes are incorporated in the emulsions. that the sensitization produced byA a given dye varies with the type yof emulsion in which it is incorporated. Furthermore, the sensitization of a given emulsion by a given dye may be altered by varying conditions in the emulsion; for example, the sensitization of a given gelatina-silver-halide emulsion may be increased by increasing the silver ion concentration or by decreasing the hydrogen ion concentration (i. e. by increasing the alkalinity) or both. Thus, the sensitization can be increasedby bathing plates, coated with a sensitized gelatino-silver-halide emulsion, in water or in solutions of ammonia.

This process of altering the sensitization of a sensitized emulsion by increasing the silver ion concentration and/or by decreasing the hydrogen ion concentration is commonly called hypersensitizatio." The method, since it involves bathingl of coated plates, is lhighly impractical for anything but specialized work, and in' addition, hypersensitized emulsions generally have poor keeping qualities.

More recently lit has been found that the sen- 40 sitization produced in an emulsion by certain spectrally sensitizing dyes can be increased by incorporating certain other spectrally sensitizing dyes in the sensitized emulsion. The effect of the mixture or combination of spctrallysen- 4- 5 sitizing dyes is more, frequently considerably It is also known sensitization produced in emulsions by simple cyanine. and ad-carbocyanine dyes. Since the conditions in the emulsion, e. g. the hydrogen ion concentration or the silver ion concentration, undergo little or no' change in my new method, I shall designate my new' method as a kind of. supersensitization. However, my new vmethod is not to be confused with that described in the above patents, because instead of employing combinations of sensitizing dyes, I employ a mixture or-combination of one V'or morei sensitizing dyes with one or-more substances which in themselves have at most but a small sensitizing effect on the emulsions. The substances which I incorporate in emulsions, in combina-f1 I shall refer to my mixtures of sensitizing dyes and acylmethylene compounds as new combinations, although I do not intend to imply that the sensitizing dyes and acylmethylene compounds are chemically combined. The acylmethylene compounds can be referred'to as the supersensitizing substances.

It is an object, of my invention, therefore, to provide new' supersenstized photographic emulsions. A further object is to provide a method of altering the sensitivity-of spectrally sensitized emulsions. A further object is to provide a process for increasing the sensitivity of sensitized emulsions. A still further object is to provide a photographic element comprising supersensitized emulsions. jects will become apparent hereinafter.

'Ihe sensitizing c yanine dyes employed in my invention sensitize, in themselves, gelatino-sil- Other more specific obver-halideemulsions between about 400 mm. and

about 720 mm. The sensitizing simple. cyanine dyes employed in my invention contain at least one pyridine or at least one quinoline nucleus, such as is the case in 2,2cyanine dyes, 5,6- benzo2,2-cyanine dyes, 2,4'-cyanlne dyes, 4,4- cyanine dyes, 2,2pyridocyanine dyes, thia-2'- cyanine dyes, benzothia-2cyanine dyes, selena- 2*-cyanine dyes, oxazolo2cyanine dyes, benzoxa-2'cyanine dyes, thia-4'cyanine dyes and benzothia-Y-cyanine dyes for example.

'The 'sensitizing carbocyanine dyes employed in my invention are ad-carbocyanine dyes, i. e.

they contain two heterocyclic nuclei linked through their alpha positions `by the trimethenyl zole nuclei, benzoxazole or naphthoxazole for ex-f ample.

While there is more than one manner of formulating and naming the materials which I employ in practicing my invention, it is believed that the formulas, systems of numbering and nomenclature used herein are in accordance with those used during the development of the art to its present stage. By the term "simple cyanine dye, I mean a cyanine dye in which two heterocyclic nuclei are linked or joined to gether by a single methenyl group. Simple cyanine dyes can be represented by the following general formulas:

wherein D represents a divalent organic group, such as a vinylene or a phenylene group, L represents a methenyl group, R and R' represent organic groups, particularly alkyl groups, X represents an acid radical and Q and Z each represent the non-metallic atoms necessary to complete a heterocyclic nucleus. I employ those simple cyanine dyes containing at least one pyridine or at least one quinoline nucleus.

By the term carbocyanine dye," I mean a cyanine dye in which two heterocyclic nucleiare linked or joined together by a trlmethenyl chain. Carbocyanine dyes of the kind where the two heterocyclic nuclei are linked by a trimethenyl chain through their alpha positions, I will call a,acarbocyanine dyes. Such carbocyanine dyes can be represented by the following general formula:

set forth under Formulas I, II and III above.

The organic heterocyclic nitrogen bases containing an alkyl group on the basic nitrogen atomv and containing an acylmethylene group in the alpha position can be represented by the following general formula:

wherein R represents an alkyl group, the atomic grouping represents an acyl group and Z represents the non-metallic. atoms necessary to complete an organic heterocyclic nucleus.

' Among the simple cyanine dyes which can be employed in practicing my invention are the following:

The 2,2'cyanine dyes which can be represented by the following formula:

N fil/5X The benzothia2'cyanine dyes which can be represented by the following formula:

-The oxazolo2cyanine dyes which can bev represented by the following general formula:

The benzoxa2'cyanine dyes which can be represented by the following general formula:

The 2,4'cyanine dyes which can be represented n by the following general formula:

' sented by the following general formula:

The thia-i'cyaninel dyes which can be repre In the above formulas'of simple cyanine dyes, R and lR represent alkyl groups and X represents an acid radical. In practicing my invention, I have found it advantageousl to employ the dyehalides, particularly the dye-iodides (where X represents iodine). However, other dye-salts can be employed, such, for example, as the chlorides,

bromides, perchlorates or Vp-toluene-sulfonates. I have further found it advantageous to employ simple cyanine dyes where R and R' represent alkyl groups of the formula CnHan+1 wherein n represents a positive integer of from one to four. The dyes wherein R and.R;' represent ethyl (02H5) groups are particularly useful in practicing my invention. Among the pseudo-cyanine (2'cyan.ine) dyes, `i.'e. those containing a quinoline nucleus, the 2,2'cyanine, the this-2'- cyanine, the se1ena2'cyanine, the 3,4-benzothia-2'cyanine, the 3,4benzoxa2'cyanine and oxazolo2'cyanine dyes are particularly advantageously `employed in practicing my invention.

Any of the simple cyanine dyes can carry on their nuclei substituents which -do not interfere with sensitizing properties, such, for example as chloro,

. bromo, alkyl, alkoxy or amino groups.

The methods of preparing the simple cyanine dyes are well known and described invarious patents and technical literature. However, the following will aid those skilled in the art in locating quickly the available information.

2,2cyanine dyes can be prepared as described by Hamer in J. Chem. Soc., page 206 et seq. (1928). 2,2'pyridocyan'ine dyes can be prepared as described by Brooker and Keyes in Jour. Am. Chem. Soc. vol. 57, page2488 et seq. (1935). Thia-2'cyanine dyes and' 5,6benzo2,2cya' nine dyes can be prepared as described by Hamer inJ. chem. soc. page 206 et seq; (192s). Selena.. l

2cyanine dyes can be prepared as described by Brooker and Keyes Jour.A Am. Chem. Soc. vol. 57, page 2488 et seq. (1935). Benzothia2'cya'nine dyes can be prepared as described by Hamer in J. Chem. Soc. page 2598 et seq. (1929). Oxazolo- 2'cyanine dyes can be prepared as described in United States Patent 1,969,446, dated August 7,

A 1934l (see also United States Patent 2,143,839,

dated January 17, 1939). Benzoxa2"cyanine Ydyes can be prepared as described in the United States-Patent 1,969,448, dated August 7, 1934.

2,4'cyanine dyes can be prepared'as described by Mills andPope in Phot. J., page 183 et seq. (1920). Still other 2'and 4cyanines are described in the copending application of Burt A Carroll and Edward P. Davey, Serial N o. 145,534, filed May 29, 1937.

Among the a,a'earboeyanine dyes which can be employed in practicing my invention are the following:

The 8alhlthiacarbocyanine dyes which can be represented by the following general formula:

The yii-alkylxelencarbocyanine dyes which can be represented by the followin! general formula:

dyes which can be represented by the following general formula:

The 8alkvlvv3,4,3f,4dibenzothiacarbocyanine dyes which can be represented bythe following general formula: j

The 8a1kyloxathiacarbocyanine dyes which can be represented by the following general formula:

The s-slkyldibenmxacarbocyamne dyes which can be represented by the following general formula:

The 2,2'carbocyanine dyes which can be represented by the following general formula:

In the above formulas of a,'a'carbo'cyanine.

dyes, R, R and R represent alkyl groups and X represents an acid radical. In practicing my invention, I have found it advantageous to employ the dye-halides, particularly the dye-iodides (where X represents iodine). dye-salts can be employed, such, for example, as the chlorides, bromides, perchlorates and ptoluene-sulfonates. I have further found it advantageous to employ carbocyanine dyes where R, R' and R" represent alkyl groups having the formula C1H2n+1 wherein n represents a. positive integer of from one to four. The dyes wherein R and R represent ethyl (CzHs) groupsy and wherein R represents methyl or ethyl are especially advantageously employed. Among the a,a'carbocyanine dyes, the 8-alkyl-a,a'carbo cyanines are advantageously employed; especially the 8-alkylthiacarbocyanine, the B-alkylselenaample, as with chloro, bromo, alkyl, alkoxy and amino groups.

The methods for preparing a,a-carbocya.nine dyes are Well known and described in various patents and technical literature. The following will aid those skilled in the art in locating quickly the available information. y

2,2carbocyanine dyes and oxacarbocyanine dyes can be prepared as described by Hamer in J. Chem. Soc., page 2796 et seq. (1927) B-alkylthiacarbocyanine dyes can be prepared as described in United States Patent 1,934,657, dated November 7, 1933. 8-alkylselenacarbocyanine dyes can be prepared` as described in United States Patent 1,990,681, dated February 12, 1935.

Among the organic heterocyclic nitrogen bases containing an alkyl group on the basic nitrogen atom and containing an acylmethylene group in However, other the 4tir-position which I employ in practicing my invention are the following:

The 1acylmethylene-2-alkylbenzothiazo1ines (1 -acylmethylene-2-alkyl-1,2-dihydrobenzothiazoles) which can be represented 'by the following formula:

The l acylmethylene-2-alkylbenzoselenazo lines (lacylmethylene-Z-alkyl-1,2-dihydrobenzoselenazoles) which can be represented 'by the following formula:

The 2 acylmethylene-1-alkyl--naphthothiazolines (2-acylmethylene-1-alkyl-1,2-dihydro-- naphthothiazoles) which can be represented by the following formula:

The 1-acyln'iethylene 2 alkyl-a-naphthothiazolines (l acylmethylene2-alkyl1,2-dihydroa-naphthothiazoles) which can be represented by the following formula:

In the above formulas, R represents an alkyl group and R' represents hydrogen or an alkyl group. I have found it advantageous to employ acylmethylene compounds wherein R and R' represent alkyl groups' of the formula CnHzHi wherein n represents a 'postive integer of from' Methods for their preparationv (other than formylmethylene) can be found for example in United States Patent 2,112,139, dated March 22, 1938. Methods for the preparation of formylmethylene compounds can be found for example According to my invention, I incorporate one or more sensitizing simple cyanie dyes of the aforesaid type and/or one or more sensitizing a,acarbocyanine dyes, together with one or more organic heterocyclic nitrogen bases containing an alkyl group on the basic nitrogen atom vand containing an acylmethylene group in the alpha position. My invention is'particularly directed to the ordinarily employed gelatino-silver-halide emulsions. However, my supersensitizing combinations can be employed in emulsions in which the carrier is other than gelatin, for example, a resinous substance or cellulosic derivative Vwhich has substantially no deleterious effect` on the light-sensitive materials. As silver halide emulsions, I include such emulsions as are commonly employed in the art, but more particularly the customarily employed silver chloride and silver bromide emulsions. The silver chloride and silver bromide emulsions may contain other salts which may be light sensitive. By way of illustration, the herein described supersensitized emulsions were prepared employing an ordinary gelatine-silver-'bromide emulsion o'i' ordinary concentration (approximately 40 grams of silver halide per liter).

The sensitizing dyes can be employed in various concentrations depending upon the effects desired. As is well known-in the art, the sensitivity conferred upon an emulsion by a sensitizing dye does not increase proportionately to the concentration of the dye in the emulsion, but rather passes through a maximum as lthe concentration is increased. In'practicing my invention the sensitizing dyes are advantageously employed in about their optimum concentrations or somesolutions in appropriate solvents.

what less, athough they may be employed in concentrations above theiroptimum concentrations.

'Ihe optimum concentration of a sensitizing dye or combination of sensitizing dyes can be determined in a manner well known to those skilled in the art by measuring the sensitivityy of a series of emulsions containing differentconcentrations of the sensitizing dye or dyes. Ordinarily, the optimum or near optimum concentration of a sensitizing dye is of the order of to 20 mg. per liter of the dye per liter of ordinary emulsion.

In practicing my invention the sensitizing dyes are ordinarily advantageously employed in concentratidns within therange of 5 to 20 mg. per liter of emulsion. The acylmethylene compounds are ordinarily advantageously employed Ain concentrations of the same order, although concentrations of from one-tenth to one hundred times the concentration of the sensitizing dyes have been employed.

In addition to acting as supersensitizers, the acylmethylene-compounds have. a tendency to reduce fog inphotographic emulsions. -As antifoggants they can be incorporated in emulsions in about the same concentrations as are advantageously employed for supersensitization, with or without sensitizing dyes.

The methods of incorporating sensitizing dyes in emulsions are simple and well known to those skilled in the art. In practicing my invention, the sensitizing dyes of my combinations can be incorporated in the emulsions separately or together with the acylmethylene compounds. It is convenient to add rst the dyes in the form of Then, the acylmethylene compounds can be added, advantageously inthe form of a solution. The solvents employed must, oi course, be compatible with the emulsions, substantially free from any deleterious eil'ect on the light-sensitive mateacylmethylene compounds. Methanol has proven satisfactory as a solvent for both the dyes and the acylmethylene compounds in practicing my invention. Acetone can also be employed. The dyes and the acylmethylene compounds are advantageously incorporated in the finished, washed emulsions and should be uniformly distributed throughout the emulsions. The following procedure is satisfactory: A stock solution of the dye or of the acylmethylene 4compound is prepared by dissolving the dye or acylmethylene compound in a suitable solvent, such as methyl or ethyl alcohol or acetone. Then, to one liter of a fiowable gelatine-silver-halide emulsion, an amount of the so-prepared stock solution, diluted somewhat with water is desired, containing the desired amount of dye or acylmethylene compound is slowly added with stirring. Stirring is continued until the dye or acylmethylene compound is thoroughly incorporated. The supersensltized emulsion can then be coated out on a suitable support, such as glass, cellulose derivative, resinous material, paper or the like, to a suitable thickness and allowed to dry. The details of such coating methods are well known to those skilled in the art.

The amount of dye or acylmethylene compound actually incorporated in the emulsion will, of course, vary from dye to dye and acylmethylene compound to acylmethylene compound, according to the emulsion employed and according to the supersensitizing effect desired. 'I'he regulation and adoption of the most economical and useful proportions will be apparent 'to those skilled in the emulsion art upon the ordinary observations and tests customarily employed in the art.. Accordingly, the foregoing procedures and proportions are to be regarded only as illustrative.y

The following combinations of sensitizing dyes and acylmethylene compounds all illustrative of combinations whichcan be employed in practicing my invention. These illustrations are not intended to be limiting.

A. 1 ethyl-Z-acetylmethylene--naphthothiazoline (1-ethyl-2-acetylmethylene-1,2-dihydro- -naphthothiazole) with one or more of the fol lowing dyes: y

rials and capable of dissolving the dyes and the iodide.

chloride.

C. 1,1'diethy12,2cyanine iodide with one orv more of the following acylmethylene compounds:

2-ethy1-1-acetylmethylenebenzothiazoline.

1 ethyl-2 formylmethylene-'-naphthothif azoline.

2-ethyl-1furoylmethylenebenzothiazoline.

2-ethyl-lacetylmethylenebenzoselenazoline.

2 formylmethylene 1,6-dimethyl-1,2 dihy droquinoline.

1i1 ethyl 2 propionylmethylenebenzothiazo ne.

D. 2,2' 8 triethyl 4,4' dichlorothiacarbocyanine bromide with one or more of the followacetylmethylene--naphthothiing acylmethylene compounds:

by the dotted curve in each figure) and showingv second the sensitivity of the same silver bromide emulsion containing a mixture or combination of the said sensitizing dye together with an acylmethylenecompound (represented by the solid 'curve in each iigui'e). The supersensitizing effeet is apparent from the curves.

In Fig. 1, curve A represents the sensitivity of an ordinary gelatino-silver-halide emulsion conconcentration of 15 mg. per'liter of emulsion.

Curve B represents the sensitivityr of the same gelatino-silver-bromide emulsion containing 15 mg. of 1,1'diethyl2,2cyanine iodide per liter of emulsion and 20 mg. of l-methyl-2-acetyl-l methylene--naphthothiazoline per liter of emulsion. 'I'he increase in green sensitivity owing to the 1-methy1-2-acetylmethylene compound is about 150%.

In Fig. 2, curve C represents the sensitivity of an ordinary gelatino-silver-halide emulsion containing 6'methyl-2,1-diethyl-3,4benzothia 2cyanine iodide in a concentration of about 2O mg. per liter of emulsion. Curve D represents 10 the sensitivity ofthe same gelatino-silver-bromide emulsion containing 20 mg. of 6methyl liter` of emulsion and 20 mg. of 1-methy1-2- acetylmethylene--naphthothiazoline per litter 15 of emulsion. The increase in green sensitivity owing to the lmethyl2-acetylmethylene compound is about In Fig. 3, curve E represents the sensitivity of an ordinary gelatino-silver-halide emulsion con- 20 taining 6-methyl2,1'diethyl-3,4benzothia2 cyanine iodide in a concentration of about 20 mg. per liter of emulsion. Curve F represents the sensitivity of the same gelatino-silver-bromide diethyl3,4benzothia2-cyanine iodide per liter of emulsion and 20 mg. of 1-methyl-2-propionylmethylene--naphthothiazoline per liter oi emulsion. The increase in green sensitivity owing to the 1methyl-2-propionylmethylene compound is 80 about 40%.

In Fig. 4, curve G represents the sensitivity of an ordinary gelatino-silver-bromide emulsion containing 2,2',8triethyl5,6,5',6-dibenzoxacarbocyanine iodide in a concentration ofl 10 mg. per 85 liter of emulsion. Curve H represents the sensitivity'of the same gelatine-silver-bromide emulbocyanine iodide per liter oi'l emulsion and 20 mg.

zoline per liter of emulsion. The increase in green sensitivity owing to the 1-methyl-2-acethymethylene compound is about 'I'he spectrograms corresponding to the figures of the accompanying drawing were made in a 45 wedge spectrograph. Each horizontal line represents an incident light intensity of about onetenth of that of the line below it. The spectrograms with and without the acylmethylene compounds were made from plates coated from. the 50 same batch of emulsion. dried and processed together.

Similarly an ordinary gelatine-silver-bromide Y emulsion sensitized with 8-methyl2,2diethyl thiacarbocyanine bromide (10 mg. per liter of 55 emulsion) showed about a 20% increase in minus blue speed, when 1-methyl-2-acetylmethylene-- naphthothiazoline (20 mg. per liter oi emulsion) lwas incorporated in the sensitized emulsion. An

sinzed 'with 4,4'd1ch1oro2,2',s-tnethylmiacarbocyanine chloride (10 mg. per liter of emulsion) showed about a- 40% increase in red sensitivity whenv 1-methyl-2-acetylinethylene--naphtho thiazoline (20 mg. per liter oi.' enmlsion) was incorporated in the sensitized emulsion. An ordinary gelatino-silver-bmmide uemulsion sensitized with 2,2',8triethylse l dide 10 mg. per liter of emulsion) showed about a 30%A increase in red sensitivity when l-methyi- 2-acety1methylene-p-naphthothiazoline (20 mg.

per liter oi' emulsion) was incorporated in the sensitized emulsion. An ordinary gelatine-silverbromide emulsion sensitized with 1.1' diethy1 u ordinary gelatino-silver-bromide emulsion sen- 60 corporated in 'the sensitized emulsion. An or dinary gelatino-silver-brom'ide emulsion sensibocyanine chloride (10 mg. per liter of emulsion) showed about a 40% increase in red sensitivity when `1-methyl2-propionylmethylene-lf-naphthothiazoline (20 mg. per liter of emulsion) was incorporated in the sensitized emulsion. Still further illustrations of the supersensitizing effects attainable according to my invention could 'be given, but the foregoing will suiiice to 'demonstrate to those skilled in the art the manner of practicing the invention.

What I claim as my invention and desire to be secured by Letters Patent of the United States is:

1. A photographic silver-halide emulsioncontaining at least one organic heterocyclic'nitrogen base containing an alkyl group on the basic nitrogen atom and containing an acylmethylene group in the position adjacent to the basic nitrogen'atom'.

2. A photographic gelatino-silver-halide emulsion containing at least one organic heterocyclic nitrogen base containing an alkyl group on the basic nitrogen atom and containing an acylmethylene group in the position adjacent to the basic nitrogen atom.

3. A photographic silver-halide emulsion containing a supersensitizing combination, of at least one sensitizing dye selected from the group consisting oi' simple cyanine dyes containing at least one pyridine nucleus, simple cyanine dyes containing at least one quinoline nucleus and amcarbocyanine dyes, together with at least one organic heterocylic nitrogen base containing an and a,a'carbocyanine dyes, together with at least one organic heterocyclic nitrogen base containing an alkyl group on the basic nitrogen atom and containing'an acylmethylene group in the position adjacent to the basic. nitrogen atom.

5. A photographic gelatino-silver-halide emulsion containing a superse'nsitizing combination of anine dye, together with at least one organic heterocyclic nitrogen base containing an alkyl group on the basic nitrogen atom and containing an acylmethylene group in the position adjacent to the basic nitrogen atom.

6. A photographic gelatino-silver-halide .emulsion. con-taining a supersensitlzing combination of at least one sensitizing 8-alkyl-.a,z'-carbocy anine dye', together with at least one organic `sisting of benzothiazole,

,-alkylthiacarbocyanine dyes,

heterocyclic nitrogen base of the following formula:

l Z CH3 R-N-c'=oH-o=o Where R represents an alkyl group and Z represents the nonmetallic atoms necessary to complete an organic heterocyclic nucleus selected from the group consisting of benzothiazole, benzoselenazole and naphthothiazole nuclei.

7. A photographie gelatino-silver-halide emulsion containing. a supersensitizing combination of at least one sensitizng pseudocyanine dye,

together with at least one organic heterocyclic nitrogen base of the following formula:

I. x (lm. R-N-d=cH-o=o wherein R represents an alkyl group of the formula CnHzn+1 wherein n represents a p`ositive integer of from one to four and Z represents the non-metallic atoms necessary to complete an organic heterocyclic nucleus selected from the group consisting of benzothiazole, benzoselenazole' and naphthothiazole nuclei.

8. vA photographic gelatine-silver halide emulsion containing a supersensitizing combination.

of at least'one sensitizing 2,2'-cyanine dye, together with at least one organic heterocyclic nitrogen base of the following formula:

wherein R represents an alkyl group of the formula CnH2n+1 wherein n represents a positive integer of from one to four and Z represents the non-metallic atoms necessary to complete an organic heterocyclic nucleus selected from the group consisting of benzothiazole, benzoselenazole and naphthothiazole nuclei.

9. A photographic gelatino-silver-halide emulsion containing a supersensitizing combination of at least one` sensitizing 1,1dialkyl-2,2'cyanine dye, the said alkyl groups each being of the formula CnHzn+1 wherein n represents a positive integer of from one to four, together with at least one organic heterocyclic nitrogen base -of the following formula:

wherein R represents an alkyl group of the formula. CnH2n+1 wherein n represents a positive integer of from one to four and Z represents the non-metallic atoms necessary to complete an organic nucleus selected from the group conbenzoselenazole and naphthothiazole nuclei.

l0. A photographic gelatino-silver halide emulsion containing a supersensitizing combination of at least one sensitizing 8-alkyl-a,a'carbo cyanine dye selected from the group consisting of 8-alkyl-3,4,3',4- dibenzothiacarbocyanine dyes, 8-alkylselenacarbocyanine dyes, .8-a1ky1-3,4,3,4'dibenzoxacar bocyanine dyes, 8-a1kyl-5,6,5,6'-dibenzoxacar bocyanine dyes, 8-alkyl-xathiacarbocyanine dyes heterocyclic nitrogen base'of the following general formula:

I,zx on. R-i-rd=cn =o wherein R represents an alkyl group of the forand 8,-alkyl-3',4'-benzoxathiacarbocya nine dyes, together with at least one organic dialkyl 8-alkyl5,6,5',6' dibenzoxacarbocyanine dyes, 2,2-dialkyl--alkylselenacarbocyanine dyes, the said alkyl groups each being of the formula gelatino-silver-halide CHm.: wherein n represents a positive integer of from one to four, together with at least one organic heterocyclic nitrogen base of the i'ollow-v ing general formula:

wherein R represents lan alkyl group of the formula CII-Inn wherein n represents a positive integer of from one to four and Z represents the non-metallic atoms necessary to complete an organic heterocyclic nucleus selected from the group consisting of benzothiazole, benzoselenazole and naphthothiazole nuclei.

EDWARD P. DAVEY. 

